1. Field of the Invention
The present invention relates to a method of manufacturing a plasmon generator for use in thermally-assisted magnetic recording where a recording medium is irradiated with near-field light to lower the coercivity of the recording medium for data writing.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head section including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head section including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider that flies slightly above the surface of the magnetic recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To solve the foregoing problems, there has been proposed a technology so-called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating the near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near a medium-facing surface of the slider.
The plasmon generator has a front end face located in the medium-facing surface. The front end face generates near-field light. Surface plasmons are excited on the plasmon generator and propagate along the surface of the plasmon generator to reach the front end face. As a result, the surface plasmons concentrate at the front end face, and near-field light is generated from the front end face based on the surface plasmons.
U.S. Patent Application Publication No. 2011/0170381 A1 discloses a technology in which the surface of a waveguide and the surface of a metallic structure (plasmon generator) are arranged to face each other with a gap therebetween, and evanescent light that occurs at the surface of the waveguide based on the light propagating through the waveguide is used to excite surface plasmons on the metallic structure, so that near-field light is generated based on the excited surface plasmons.
Part of the energy of light guided to the plasmon generator through the waveguide is transformed into heat in the plasmon generator. Part of the energy of near-field light generated by the plasmon generator is also transformed into heat in the plasmon generator. The plasmon generator thus increases in temperature during the operation of the thermally-assisted magnetic recording head. The plasmon generator is typically formed of a polycrystal of metal such as Au or Ag having a high electrical conductivity. An increase in the temperature of such a plasmon generator would cause a plurality of crystal grains constituting the metal polycrystal to aggregate and grow, and this may result in a deformation of the plasmon generator. The deformation of the plasmon generator takes place, for example, in a manner such that the front end face of the plasmon generator is significantly recessed relative to the other parts of the medium-facing surface. Such a deformation of the plasmon generator would cause the plasmon generator to be unable to provide the desired heating capability thereof. Thus, conventional plasmon generators have the drawback of being low in reliability.